The dispersion relations of plasmons in a simplified system of CuO2 layers and Cu−O chains

A simplified model for YBa₂Cu₃O₇ system composed of CuO₂ layers and Cu–O chains has been calculated with the long range effect of the all-neighbors Coulombice-e interactions taken into consideration. Dispersion relations have been worked out and discussed. The most striking consequence from the all-neighbors interaction is that the plasmons have, in the long wavelength limit, in addition to the usual vanishingly small two-dimensional acoustic plasmon energies which result from only nearest neighbor interactions, a non-zero _P ^* consistent with the bulk plasma frequency of a three dimensional system. The data of an optical reflectance from an EELS experiment has been refitted based on calculated results for plasmon dispersion relations in the YBa₂Cu₃O₇ system.     

Hybrid approach to the synthesis of highly luminescent CdTe/ZnS and CdHgTe/ZnS nanocrystals

We report the synthesis of highly luminescent CdTe/ZnS and CdHgTe/ZnS core/shell semiconductor nanocrystals (NCs). A hybrid of two synthesis routes leads to novel nanocrystal compositions and small core/shell sizes (4-5 nm) that emit in the far-red and near-infrared regions. These particles exhibit higher resistance to oxidation and photobleaching, have high quantum yields, and could be used for biological labeling and imaging.     

Structures of three substituted pentacyclo[5.4.0.02, 6.03, 10.05, 9]undecanes and a computational analysis of bond lengths

5-Methyl-2-phenylpentacyclo[5.4.0.0^{2, 6}.0^{3, 10}.0^{5, 9}]undecane-8, 11-dione,5-methyl-2-phenylpentacyclo [5.4.0.0^2,6.0^3,10.0^5,9]undecane-8-one-11-ol,and 5-methyl-2-phenylpentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecane-8,11-diol are three cage compounds which differ only in the oxidation state at C(8) and C(11). The three compounds contain a four-membered, a six-membered, and four five-membered rings fused into a cagelike structure. An X-ray structure analysis shows the C(1)-C(7) and C(9)-C(10) bonds in the diketo cage to be 1.606(2) and 1.586(2) Å, which are significantly longer than in the other two molecules. In order to assess the effects of strain, steric, and electronic factors in these compounds, we investigated the unsubstituted parent cage compounds and a series of derivatives by molecular mechanics (MM3), AMPAC (AM1), MOPAC (PM3), and GAUSSIAN 90 calculations. These data suggest that dipolar through space interactions are responsible for the bond elongation and not a _– ^* interaction, which has been postulated in parallel-systems originating from a common bond. A small degree of _– ^* through-bond interaction may contribute to the lengthening in the dimethylene cage analogues.     

Permanently oriented antibody immobilization for digoxin determination with a flow-through fluoroimmunosensor

This paper reports a new flow-through fluoroimmunosensor, the function of which is based on antibodies immobilized on an inmunoreactor of controlled-pore glass (CPG), for determination of digoxin, used in the treatment of congestive heart failure and artery disease. The immunosensor has a detection limit of 1.20 microg L(-1) and provides high reproducibility (RSD=4.5% for a concentration of 0.0025 mg L(-1), and RSD=6.7% for 0.01 mg L(-1)). The optimum working concentration range was found to be 1.2 x 10(-3)-4.0 x 10(-2) mg L(-1). The lifetime of the immunosensor was about 50 immunoassays; if stored unused its lifetime can be extended to three months. A sample speed of about 10-12 samples per hour can be attained. Possible interference from substances with structures similar to digoxin (morphine, heroin, tebaine, codeine, pentazocine and narcotine) was investigated. No cross-reactivity was seen at the highest digoxin: interferent ratio studied (1:100). The proposed fluoroimmunosensor was successfully used to determine digoxin concentrations in human serum samples.     

Picosecond time-resolved cars in isotopically mixed crystals of benzene

Time-resolved coherent anti-Stokes Raman experiments are reported for the benzene crystal 991 cm^?1 mode and in mixed C₆H₆/C ₆D₆ crystals. Addition of C₆D₆ results in an increase in the rate at which the excitation is trapped. This is explained by the recent theory of Velsko and Hochstrasser which predicts that the trapping rate should undergo a maximum at some isotopic impurity concentration, consistent with observations from time and frequency domain studies. A proper convolution procedure for CARS experiments in the time domain is presented.     

Preparation and photocrosslinking behaviors of polyesters derived from trans-2,2′-dihydroxystilbene

The monomer, trans-2,2′-dihydroxystilbene (DHS), has been prepared by asymmetric photocleavage (254 nm) of coumarin dimer acid derived from coumarin dimer. Four new polyesters are successfully synthesized by interfacial polycondensation of the DHS with adipoyl chloride, azelaoyl chloride, sebacoyl chloride, and dodecanedioyl dichloride, respectively. The reduced viscosities of the polyesters decrease from 0.32 to 0.11 dL/g as the number of methylene unit in diacid chlorides increases from 4 to 10. From DSC investigation, it is found that the polyesters are semi-crystalline polymers with T_m = 39–192°C. Under 350 nm light, photocrosslinking behavior in solution and film-state is investigated by UV spectral change with irradiation time (350 nm). The photoreactive stilbene chromophores in the main chain dimerize to form cyclobutane derivatives, and lead to crosslinking of the polyesters. Photosensitivity in the film state has also been evaluated by their characteristic curves. Polyester from dodecanedioyl dichloride ( 5d ) exhibits the highest initial reaction rate and ultimate crosslinking ratio. © 1995 John Wiley & Sons, Inc.     

A Straightforward Synthesis of Polythiophene-fused-3-sulfolenes from Methyl 3-Hydroxy-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylate

A straightforward synthesis of substituted polythiophene-fused-3-sulfolenes from the readily prepared methyl 3-hydroxy-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylate will be presented. Upon thermolysis in the presence of N-phenylmaleimide, these new substrates serve as precursors of reactive polythiophene o-quinodimethanes to give the corresponding Diels-Alder adducts in high yields.     

Remarks on the Convergence Rate of the Spectral Distributions of Wigner Matrices

In this remark, we show that under the assumption of the finite fourth moment elements in the empirical spectral distribution of a large Wigner matrix converges to the Wigner semicircular law in probability of the order O(n ^–1/3).